Method of making a spark plug



Nav.. l, 19407 A. QHASTINGS, Jia' METHOD OF MAKING A SPARK b.13h-i12 l Filed April 29, 1937 INVENTOR Patented Nov. 19, 1940 UNITED STATES PATENT OFFICE Claims.

'Ihe invention has for one of its objects to provide a novel and superior method of making a spark plug of the general type forming the subject matter of my United States Patent No.

Il 2,069,951, issued February 9, 1937, by which insulating defects and unintentional short circuiting of the plug may be reduced to a minimum.

With these general objects in View, and such others as may hereinafter appear, the invention consists in the method of making the spark plug, hereinafter described and particularly dened in the claims at the end of this specification.

In the drawing illustrating different embodiments of the invention, Fig. l is a vertical sectional View of a shielded spark plug adapted for aeronautical use; Figs. 2, 3 and 4 are vertical section views of a modified form of spark plug illustrating different connections between the 20lead-in cable and the inner electrode of the plug;

Fig. 5 is a plan View of a ferrule designed for use in connection with the present electrical connection between the lead-in cable and the inner electrode of the plug; Fig. 6 is a vertical sectional detail of the upper end portion of a plug showing the ferrule illustrated in Fig. 5 in operative position; and Fig. '7 is an inverted sectional view of the plug.

One feature of the present invention contemplates a no-vel andimproved construction for providing a novel connection between the leadin wire or cable and the inner electrode of the spark plug, by which a most satisfactory electrical connection may be maintained while reducing to a minimum the cost of manufacture of the parts necessary for the establishment of such electrical connection. In the preferred embodi ment of the invention, the upper portion of the plug is provided with a socket into which the end of the lead-in cable may be forced in tightly fitting relation. A pin, electrically connected to the inner electrode, is arranged to project from the bottom of the socket whereby when the leadin cable is pushed into the socket the pin is forced into the electrical conductor or wiring of the cable. Provision may and preferably will be made for securing the cable in its operative position although for some purposes the frictional contact of the outer surface of the cable and the lateral walls of the socket are sufficient to retain the parts in operative position during use of the plug.

Another feature of the invention resides in a shielded spark plug of a novel and simplified vconstruction which lends itself particularly for use as an aeronautical plug. The outer electrode of the plug is preferably elongated to form a metallic protecting shell for shielding the plug, and the connection between the lead-in cable and the inner electrode of the plug.

The position of the lead-in cable between the spark plug and the usual armor cable may be shielded by a metallic elbow, the lower end of which may be secured to the upper end of the shielded plug, to provide a complete shield for 10i' both the cable and plug.

Still another feature of the invention resides in a novel ,method of making a spark plug of the general type illustrated in my Patent No.

2,069,951, above referred to, by which insulating vvv defects and unintentional short circuiting between the inner and outer electrodes may be reduced to a minimum, as will be hereinafter described.

Referring now tothe drawing, the different features of` the invention have been illustrated as embodied in spark plugsof the type forming the subject matter of my United States Patent No. 2,069,951, dated February 9, 1937, and which in general comprise an outer metallic electrode sulating member is preferably thin and arranged with the inner electrode to substantially fill the bore within the outer electrode and to terminate in substantially the plane of the outer electrode to the. end that during the operation of the plug,

sparksI are caused to traverse across the end y of the insulating member. The upper end of the insulating member I4 is preferably arranged to extend above the outer electrode and the upper portion of the insulating member I4, as well as the upper portion of the inner electrode I2, may 40.

and preferably will be enclosed within a second or auxiliary protective insulating member I8. The latter may comprise a molded insulating composition such as a phenolic-formaldehyde resinous composition or other suitable insulating material.

In accordance with one feature of the present invention the inner electrode I2 has electrically connected therewith a contact member herein shown as comprising the extended upper end portion 22 of the inner electrode I2 and which is preferably shaped to facilitate its being forced into the strands making up the conductor 24 of the lead-in cable when the cable is positioned for connection with the spark plug. As herein 5L 50the plug I8.

for the cable and the plug, the member 42 also.

shown, the protective insulating member I8 is provided with a socket 26 preferably of a size to closely t the end of a standard lead-in cable and the upper end 22 of the electrode I2 is arranged to project upwardly from the bottom of the socket 26. When the cable end is forced into the socket, the end portion 22 of the inner electrode is forced into the electrical cable conductor 24 establishing a most satisfactory electrical connection.

Referringnow to Fig. 1, in whichthe present invention is illustrated as embodied in a spark plug for aeronautical use, the construction of the plug is such that the outer electrode I is elon-` gated to form a protective metallic shell for shielding the plug and the connections between the lead-in cable 28 and the inner electrode I2 is provided. vThe elbow is secured to the Vtop of` the spark plug by a nutv34 which is screwed down over the top ofthe plug and over a flange 36 on the end of the elbow.

Provision is made for retaining the lead-in cable 28 within the socket 26 and in contacting relationship with the .upperend of the .electrode 22, and for this purpose a split eyelet 38 is placed around the cable under the flange 36 of the elbow between the flange and .the top of the spark plug. The leyelet may be provided with a tapered portion 46, as illustrated, so that when the nut 34 is tightened down the portion 4B of the eyelet will be forced into and clamp the lead-in cable V-to thereby retain the cable in operative position 45'ffmemb'ers are shown in Figs. 3 to 6 inclusive,

wherein Fig. 3 illustrates an outer .insulating member 42, made of rubber or other resilient materiall which is stretched around the lead-in cable 28 and over the top of the body portion of In addition to serving as a retain-er serves as a covering to-keep out dirt and moisture.

Referring now to Fig. 4, another method of `securing the lead-in cable to the plug comprises a metal cap or .ferrule 44 which is placed over the end of the lead-in cable 28 and is secured thereto by prongs 46 extending inwardly from the cap which are forced intothe covering of thecable.

upper end and this enlarged portion 48 is adapted to snap into a groove 56 provid-ed in the socket 26, when the members are in operative position.

The end of the inner electrode 22 extends through, the end of the cap to contact with the conductor A still further modification, asv illustrated in` Figs. and 6, comprises a ferrule 52, provided with prongs 54, which issnapped over the end of the 'body portion I8. The prongs 54 extend downwardly and serve to retain the lead-in cable in the desired operative position.

In the spark plug illustrated herein, the inner electrode I2 is, .at,its 'upper end portion, sur- 'irounded and protected by a body of insulating The diameter of the cap is enlarged near itsv material comprising preferably a molded insulating material such as Bakelite. The portion of such insulation above the end of the tubular insulating member I4 and around the inner electrode I2 comprises in effect a bridge between the top of the insulating member I4 and the bottom of the socket 26. In the manufacture of the plug, a hole is preferably formed in the bridge 56 of a size at least no greater than the size of the inner electrode I2 so that the inner electrode may extend therethrough with a driving lit and produce a gas-tight joint atthis point.

In order to further insure against unintentional short circuiting of the plug by passage of current from .the inner electrode around the outer surface of the tubular insulating member I4 and between it and the insulating body I8 and thence to the top of the outer electrode I0, I prefer to provide a continuous iilm or layer 60 of cement between the inner electrode .and the inner wall of the tubular insulating member I4 and also a layer of cement 62 between the outer sur-- face of the insulating member I4 and the surrounding insulating body I8. In practice, the preferredv method of cementing and assembling the component parts of the' plug, as will be de-l clearly shown in the drawing, and as a result of the method of cementing and assembling these parts of the plug, the portions 60, 62, 64 of the herein referred to, the porous cement body tended to become carbonized and to become a conductor so that the plug frequently failed because of a short circuit from the inner electrode around the surface of the insulating tube I4 to the upper end of the outer electrode Ill, the 'body of cement between these parts functioning as a conductor. I have found that certain organic cements having Bak-elite and other similar resinous materials as a base may be used with particular advantage in the manufacture of a spark plug and when so used the cement hardens into a non-porous and ecient insulating lm which satisfactorily prevents unintentional short circuiting of the plug in the manner above described.

In order to assemble the component partsof the plug and at the same time to insure that the films 60, 62 and 64 of cement will be of a nonporous nature and free from air pockets, I not only prefer to employ a non-porous uid type of cement such as an organic ,Bakelite cement or other resinous cement, but I have also found it desirable to introduce the cem-ent into the bo-re or hole 21 which is formed within the insulating body I8 when the latter is molded, prior to the insertion of both the insulating tube I4 and the center or inner electrode I2 therein, so asto form in effect a reservoir of cement within the bore or hole 21 through which the electrode I2 and tube I4 may be subsequently passed to be coated when being driven into operative positions with the cement which hardens into a continuous non#- porous film.

When such a ce-1 ment was used in a spark plug of the character.

' In practice it is preferred to first mold the insulating body I8 about the upper end of the outer electrode ID and then in order to conveniently introduce the cement into the bore or hole 21 hof the insulating member I8, it is preferred toinvert the insulating member I8 and outer electrode II] into a position such as is shown in Fig. 7 and tointroduce the fluid cement into the bore 2l by means of a hypodermic needle or other suitable hollow instrument extended upwardly through the preformed center electrode hole in the bridge 55 in the molded insulating body I8. The center electrode is then inserted from the upper end of the plug into the small hole in the bridge 56 and driven downwardly into place, the hypodermic needle being withdrawn as the center electrode is driven through the bridge 56. Thereafter the insulating tube I4 is introduced and forced into position. The advantages of this procedure are that the formation of air pockets is entirely prevented and the operative parts are coated with a continuous film of the cement which, when hardened, produces the non-porous efficient insulating layers 60, B2, 64 illustrated herein.

From the foregoing description it will be observed that the present connection between the lead-in cable and the inner electrode is conducive to the maximum economy in the manufacture of the plug. The number of small parts which have heretofore been required in the manufacture of prior spark plugs are eliminated. In addition to the economy .of manufacture of the present plug, it will be observed that the current in order to leak from the inner to the outer electrode is obliged to travel an extremely long path, thus reducing liability of kleakage to a minimum and enabling the plug to function under moisture conditions in a most satisfactory manner. The present type of electrical connection not only affords a more intimate and superior electrical connection but also is subst-antially moisture and dirt proof.

The shielded construction of plug illustrated in Fig. l and herein described, may be economically manufactured and affords a complete shield for both the plug and electrical connections between the plug and the inner electrode.

Nhile the different embodiments of the invention have been herein illustrated and described, it will be understood that the invention may be embodied in other forms within the scope .of the following claims.

Having thus described the invention, what is claimed is:

l. The method of making a spark plug of the type having an inner electrode, an outer electrode, a preformed elongated tubular insulating member of substantially uniform thickness throughout its length positioned between said electrodes, and an outer protective insulating member for the upper portion of the spark plug, comprising moulding the outer protective insulating member around portions of the outer electrode to form a unit therewith, inverting the unit thus formed, providing a reservoir of fluid cement within the unit and then forcing rst the inner electrode downwardly through said reservoir into operative relation with said outer electrode and protective insulating member and thereafter forcing said insulating member through the reservoir and over the inner electrode whereby both the inner electrode and the vouter and inner surfaces of said insulating member are provided with coatings of cement.

2. The method of making a spark plug of the type having an inner electrode, an outer electrode, a preformed tubular insulating member of substantially uniform wall thickness positioned between said electrodes, and an outer protective insulating member moulded upon the upper end of the outer electrode and extending for a substantial distance above the same, comprising moulding said outer protective insulating member upon said outer electrode and forming a chamber therein having a bottom wall, the bottom wall .of the chamber being provided with an opening through which the inner electrode is adapted to extend, forming a reservoir of fluid cement within said chamber and introducing the inner electrode and said insulating tube into the unit and through said reservoir of cement whereby to coat the outer and inner surfaces of said tubular insulating member with cement as well as the surface of said inner electrode.

3. The method of making a spark plug of the type having an inner electrode, an outer electrode, a preformed tubular insulating member of substantially uniform wall thickness positioned between said electrodes, and an outer protective insulating member moulded upon the upper end of the outer electrode and extending for a substantial distance above the same, comprising moulding the outer protective insulating member upon the upper end of said outer electrode and forming a chamber within said insulating member, introducing fluid cement into the chamber to form a reservoir thereof and then forcing the tubular insulating member and the inner electrode into operative relation with said outer protective insulating member and through said reservoir of cement whereby to coat the inner electrode and both the outer and inner surfaces of said tubular insulating member with cement.

4. The method of making a spark plug of the type having an inner electrode, an outer electrode, a preformed tubular insulating member of substantially uniform wall thickness positioned between said electrodes, and an outer protective insulating member moulded upon the upper end of the outer electrode and extending for a substantial distance above the same, comprising moulding said outer protective insulating member upon said outer electrode and forming a chamber therein having a bottom wall, the bottom wall of the chamber being provided with an opening through which the inner electrode is adapted to extend, moving a tubular member through said opening and in a direction toward the outer electrode, forcing a fluid cement through said tube into said chamber to form a reservoir of cement, then moving the inner electrode through the chamber in the direction opposite to the aforesaid direction and withdrawing said tube simultaneously with the movement of said inner electrode through the opening in the bottom wall of lthe chamber in the protective insulating member and moving the tubular insulating member through said reservoir of cement and into operative position whereby to coat both the outer and inner surfaces of said tubular insulating member with cement as well as the surface of the inner -'electrode.

5. The method of making a spark plug of the type having an inner electrode, an outer hollow electrode, a preformed elongated tubular insulating member of substantially uniform thickness throughout its length positioned between said electrodes, and an outer protective insulating member for the upper portion of the spark plug,

comprising molding the outer protective insulating member around portions of the outer hollow'r electrode to form a unit therewith and tov provide a socket atone end of said unit opposite said 'outer electrode, utilizing the end of said unit having said hollow outer electrode as a reservoir, introducing fluid cement into said reservoir, forcing the inner electrode downwardly through said reservoir-and .cement until the advancing end thereof projects into said socket and forcing said insulating tube into said reservoir in substantially concentric relation with said inner electrode, whereby a layer of cement is provided between said insulating member and said inner and outer electrodes, respectively.

1 ARTHUR C. HASTINGS, Jn. 

